Studied by 25 peoplenervous system
consists of brain, spinal cord, and nerves; functions to communicate
central nervous system
structural/functional center of entire NS
consists of brain and spinal cord
integrates sensory information, values, and initiates outgoing response
peripheral nervous system
nerves that lie in “outer regions” of NS
Afferent division
consist of all incoming sensory pathways; towards CNS
efferent division
consists of all outgoing motor pathways; away from CNS→targets
somatic nervous system
carries information from somatic effectors (skeletal muscles)
carries feedback info. to somatic integration centers in CNS
autonomic nervous system (ANS)
efferent division of ANS carries info. to the autonomic/visceral effectors (smooth and cardiac muscles/glands)
sympathetic division
prepares the body to deal w/immediate threats to the internal enviorment; fight or flight response
parasympathetic division
coordinates the body’s normal resting activities; rest and repair division
visceral sensory division
carries feedback info. to autonomic integrating centers in the CNS
Glia (neuroglia)
support the neurons; 5 major types
astrocytes
in CNS
star shaped; largest and most numerous type of glia ; cell extensions connect to both neurons and capillaries; transfer nutrients from blood to the neurons; form tight sheets around brain caps. constitute the blood-brain barrier
microglia
in CNS
small, stationary cells; in inflamed brain tissue; they enlarge and move, and carry on phagocytosis
ependymal cells
in CNS
resemble epithelial cells and form thin sheets that line fluid-filled cavities (cerebral spinal fluid) in the CNS; some produce fluid, others aid in circulation of fluid
oligodendrocytes
in CNS
smaller than astrocytes with fewer processes; hold nerve fibers together and produce myelin sheet around axons
Schwann cells
in PNS
found in peripheral neurons; support nerve fibers and form myelin sheets
nuerilemma
formed by cytoplasm of Schwann cell, wrapped around the myelin sheath; essential for nerve regrowth
satellite cells
Schwann cells that cover and support cell bodies in the PNS
nuerons
excitable cells that initiate and conduct impulses that make possible all nervous system functions
perikaryon
cell body; ribosomes, rough er, Golgi; provide protein molecules (neurotransmitters) needed for transmission of nerve signals from one neuron to another
neurotransmitters are packaged into
vesicles
mitochondria
provide energy (ATP)
dendrites
each neuron has 1 or more; conduct nerve signals to the cell body of neuron
dendritic spines
small, knoblike protrusions on dendrites of some brain neurons; serve as connection points for axons of other neurons
axon
a single process extending from axon hillock, sometimes covered by myelin sheath; conduct nerve impulses away from the cell body of neuron
axon hillock
where action potential is generated
telodendria
distal tips of axons
axon varicosities
swellings that make contact with other cells
cytoskeleton
microtubules/filaments, and neurofibrils; allows rapid transport of small organelles
functional regions of neuron
input zone; summation zone; conduction zone; output zone
input zone
dendrites and cell body
summation zone
axon hillock
conduction zone
axon
output zone
telodendria and synaptic knobs of axon
structural classification of neurons
according to number of processes extending from cell body
multipolar
one axon and several dendrites
bipolar
one axon and one dendrite; least numerous kind of neuron
unipolar
one process comes off neuron cell body BUT divides almost immediately into 2 fibers; central/peripheral fiber
afferent (sensory) neurons
conduct impulses to spinal cord or brain from receptors
efferent (motor) neurons
conduct impulses away from spinal cord or brain toward muscles or glandular tissue TO effectors (muscle or glandular tissue)
reflex arc
signal conduction route to/from CNS, with the electrical signaling beginning in receptors and ending in effectors
three neuron
most common; consists of afferent neurons, interneurons, and efferent neurons
two neuron arc
simplest form; consists of afferent and efferent neurons
synapse
where nerve signals are transmitted from one neuron to another; 2 types- electrical and chemical
chemical synapse
typical in adult; located at the junction of the synaptic knob of one neuron and the dendrites/cell body of another neuron
nerves
bundles of peripheral nerve fibers held together by several layers of connective tissue
endoneurium
delicate layer of fibrous connective tissue surrounding each nerve fiber
perineurium
connective tissue holding together fascicles (bundles of fiber)
epineurium
fibrous coat surrounding numerous fascicles and blood vessels to form a complete nerve
tracts
within the CNS, bundles of nerve fibers
white matter PNS
myelinated nerves
white matter CNS
myelinated tracts
gray matter
composed of cell bodies and unmyelinated fibers
gray matter CNS
nuclei
gray matter PNS
ganglia
mixed nerves
contain sensory and motor neurons
mature neurons
incapable of cell division; damage to nervous tissue can be permanent; limited capacity to repair themselves
repair of nerve fibers
if damage is not extensive; cell body and neurilemma are INTACT; scarring has not occurred; nerve fibers can be repaired
stages of repair of axon in peripheral motor neuron
–After injury, distal portion of axon and myelin sheath degenerates
–Macrophages remove the debris
–Remaining neurilemma and endoneurium form a tunnel from the point of injury to the effector
–New Schwann cells grow in tunnel to maintain a path for axon regrowth
–Cell body reorganizes its Nissl bodies to provide the needed proteins to extend the remaining healthy portion of the axon
–Axon “sprouts” appear
–When sprout reaches tunnel, its growth rate increases
Skeletal muscle cell atrophies until nervous connection is reestablished
astrocytoma
most common brain tumor
ependymoma
surrounds ventricles of brain
acoustic neuroma
surrounds neurons for hearing and balance
neurofibromatosis
genetic; skin spots; neuromas
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